My parents current X4 is quite noisy.
The X1.1 they have is only slightly quieter.
I think the X1 machines are quietest and easiest to push. My parents also have one of those, not sure if the carbon brushes have seated properly as it always smells slightly of ozone.
I need to get better at fixing motors as I've thrown at least 5 £<10 eBay X1 uprights away because the motors were dead. I can never get the fan casings off.
The current X4 was £10.50, it was clogged with hair and lacking a foot pedal, been going for 6 years with my parents.
X1.1 was similar for £10, needed a foot pedal. Height adjustment is broken and the brushroll gets noisy when it's hot, so I assume a bearing there.
X1 was a part of a pair of which I changed the brushes and used for a while. The white one lasted <6 months before the motor started slowing, I assume bearing was beginning to seize. Grey one still exists.
The remaining X1 machines I scrapped were part of a job lot I didn't have time or space for.
The original X4 we had was used from eBay and lasted about 4 months before it started slowing down and smelling of ozone. Sold it on eBay, the buyer replaced the bearing and re-sold it.